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As far as I know the 'D1' drivelogic setting should start your off in 2nd most of them time (I have to confess that I dont drive in D1 myself and my reference is from the DCT on the M3), especially if the transmission is expecting your next start to be slow. I think part of the inconsistancy youre seeing may be your driving style confusing the DCT. From what I remember, the DCT does have some level of adaptive programming built in. It doesnt generally expect an accelerator mash from stand still in 'D1', but, if you do it once, it might go down to 1st the next time you stop thinking you may do it again. As far as shifting down from 2->1 during hard acceleration, I would figure it doesnt do that in order to avoid heavy wear on the odd numbered clutch (and there would be insane pressure on the clutch plate if you tried to shift down in the big gears while pulling a ton of torque from the engine) or to avoid a safety issue with the rev limiter. The DCT behaviour will also vary with operating temperature. If the transmission is either too cold or too hot (cant remember which one) it wont start from 2nd even in 'D1'.
As far as the efficiency settings go, always take them with a grain of salt. The driving style will impact fuel consumption much more than the drivelogic setting. If you intend on accelerating fast, you may actually burn more fuel in 'D1' than a more aggressive setting simply because the shift points may result in the acceleration taking longer.
So, I think the behaviour youre seeing may just be the intended behaviour of the transmission, but, a lot of this is speculation and someone in the know may be able to fill the both of us in better.
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